Dr. Petko Valtchev, University of Quebec in Montreal, Canada, Expert in Advisory Capacity

Abstract: Distributed Ledger Technologies (DLT) have been receiving a lot of attention from both academia and industry in the past few years. With over 10 years since it was released to the public, Bitcoin remains the most famous example of a blockchain-based distributed ledger technology. The work presented in this dissertation proposes a series of enhancements to the Bitcoin and Ethereum protocols by focusing on the most basic component: the transaction. By investigating the life cycle of a transaction in these popular blockchain systems, several proposals are presented in this work to tackle some of the challenges under active research by the blockchain community.

The first Chapter will provide an introduction alongside some key components in the field of blockchain systems. Chapter 2 will provide an overview of the most common blockchain protocols in use, followed by a survey of related work in some of the most active fields regarding the topic of decentralised ledger technologies. Chapter 3 will present Beltran’s work on the transaction selection policies in Bitcoin and how these can be used to detect anomalous mining pool behaviour. Chapter 4 will focus on the transaction validation phase of Ethereum and show how this can be exploited as a mining strategy by mining pools to increase revenue. Chapter 5 will present a compression mechanism for the Ethereum blockchain based on the recycling of bytecode from previously deployed contracts. Chapter 6 will propose mint centrality, a new centrality measure for the Bitcoin transaction graph that focuses on the minting and mixing of coins in the system. Finally, Chapter 7 will present some final conclusions on Beltran’s work and suggest future work directions.